Direct turn rotary step attenuator



J 1967 B. SCHWARTZ DIRECT TURN ROTARY STEP ATTENUATOR Filed Aug. 24, 1965 INVENTOR. BERNARD SCHWARTZ AT T0 R N EY United States Patent New Jersey Filed Aug. 24, 1965, Ser. No. 482,125 3 Claims. (Cl. 333-81) This application is a continuation-in-part of my copending United States patent application Ser. No. 305,447, filed Aug. 30, 1963, now United States Patent No. 3,219,953, entitled, Direct Turn Step Attenuator.

This invention relates to microwave step devices and more particularly relates to novel direct-turn step devices.

In the above copending patent I have provided a novel mechanism for adjusting the pad positions of a coaxial turret attenuator by means of rotation of a single knob. The present invention pertains to the specific structure of the stepping mechanism employed in my previous invention and furthermore incorporates certain improvements therein.

This invention and the invention of my above copending patent provide means for eliminating the pull-turn-push motion of the control shaft of a step attenuator of the type shown in Harges et al. United States Patent No. 2,848,693 entitled Step Attenuators.

The mechanism of Harges et al., includes a pair of movable plate members spaced apart. An assembly of attenuator pads are mounted between the plate members. Each of a pair of terminal connectors is mounted on one of the plate members so that the terminals may be selec tively engaged with any one of the attenuator pads across its terminal ends. The plate members are coupled so that they may be spaced apart by moving the control shaft axially to disengage the connectors from the selected pad. Then, the control shaft may be turned to adjust the position of the assembly. By driving the shaft in the reverse direction the connectors may be reengaged with a newly selected pad. Thus, in Harges et al., the control shaft requires a complex motion of disengaging by pulling, turning the assembly, and reengaging by pushing. For the purpose of facilitating manual control and motor control of the control shaft and assuring that the cycle of stepping the mechanism from one pad position to another is com pleted, it is desirable that the control mechanism should respond to a simple rotary motion and that it be spring biased into its normal operating position.

In my copending patent, I have broadly described a direct turn stepping system and a direct turn stepping mech anism which permits making such adjustments. This in vention relates to the specific structural detail of the mechanism including a detent ring and pin arrangement combined with a bisymmetrical cam which provides proper indexing of the cam and the central shaft on which the assembly is mounted as well as retaining the end plates spaced apart during rotation of the assembly of pads. In another aspect of this invention I have provided for tapering the end of the indexing pin and shaping of the surfaces of the cam ring indexing notches to provide less resistance to sliding of the pin across the surfaces of the ring. In still another aspect of this invention I have provided a detent mechanism for the assembly of pads for the purpose of accurately locating them comprising a spring biased button for locking the assembly by insertion within accurately aligned and properly shaped apertures in the assembly.

Preferably the apertures have outwardly inclined edges with a sharp peak therebetween to provide a snap action displacement of the button which preferably has a rounded contour thereby enhacing the tendency to snap-action operation of the turret detent. Further objects and advantages of this invention are described below in connection with reference to the appended drawings wherein:

FIG. 1 is a plan view of an improved direct turn step attenuator in engaged position,

FIG. 2 is a front elevational perspective view of fragments of the attenuator shown in FIG. 1 in disengaged position,

FIG. 3 shows a modified detent ring and detent pin in disengaged position,

FIG. 4 is a fragmentary perspective view of the detent ring shown in FIGS. 1 and 2.

Referring to the drawings, the step attenuator includes a plurality of attenuator components in the form of pads 15 of different db attenuation values. The pads 15 are arranged equidistantly, in a circular rotatable carriage assembly 16, as seen in FIGS. l-3, about a central shaft 17 co-axial with the axis of the assembly 16. The pads 15 are supported as an integral assembly 16 by end discs 18, 19 each containing a ring of apertures 20, 20 into which the pad end shoulders, of reduced diameter, are mounted.

The attenuator also includes stationary end plates 21, 22 interconnected by spaced longitudinal tie rods 23, 24, etc. of equal length and threaded at their respective ends to receive screws 26 for fastening with end plates 21, 22. The outer envelope of the step attenuator is fixed, determined essentially by the end plates 21, 22 held parallel and in fixed spaced relationship by the tie rods 23, 24.

The attenuator contains two connector terminals 30, 31. Each of the terminals 30, 31 has a threaded collar 32 for engagement with the threaded bushing of a connector (not shown) at the ends of connecting flexible external coaxial cables. The central connections of these cable connectors engage the sockets of the terminals 30, 31 respectively, in the usual manner. The terminals 30, 31 are right-angled in shape with extensions 33, 34 located within recesses in movable connector plates 35, 36 as seen in FIG. 1. Set screws (not shown) ensure firm engagement of the connector terminals 30, 31 with their respective connector plates 35, 36.

Axial displacement of the plates 35, 36 moves the respective connector terminals 30, 31 in the axial direction of said plates. However, the firm engagement of the respective flexible coaxial cables with the connector termi nals 3t), 31 in no way interferes electrically or mechanically with the high frequency microwave circuit in which the step attenuator of the invention is included with such coaxial cables. Each terminal 30, 31 has inwardly projecting connector sections 40, 41 respectively coaxial with the respective extensions 33, 34.

The connector sections 40, 41 comprise resilient externally slotted conductors for engagement with the end terminals of the atenuator pads 15. The sections 40, 41 are in axial alignment across the step attenuator, in order to be engaged selectively with the longitudinal ends of selected individual attenuator pads. The sections 40, 41 are at ground potential with respect to the outer conductors of their respective terminals 30, 31 and with ground of the step attenuator assembly. The sections 40, 41 are adapted to make firm mechanical and electrical connection with the outer cylindrical conductors of any pad 15 to which they are connected. In the interior of the respective sections 40, 41 are central connecting pins (not shown) for engagement with the corresponding central connecting conductors of the attenuator pads, as will be understood by those skilled in the art.

Longitudinal displacement of the terminals 30, 31 inwardly effects engagement of the respective connector sections 40, 41 with a selected attenuator pad 15. The central connecting conductors of the selected pad 15 thereupon become electrically interconnected with the central pins of terminals 30, 31, respectively, and in circuit with the coaxial cables to the step attenuator. FIG. 1 shows the step attenuator in such electrically engaged position, with the movable connector plates 35 and 36 in their innermost position and with the sections 40, 41 in engagement with a selected attenuator pad 154:.

The movable connector plates 35 and Man operated in unison, but in opposite directions. The attenuator pad assembly 16 is held in fixed axial position in the step attenuator. Rotational displacement of the carriage assembly 16, by means of the central shaft 17, positions a desired attenuator pad in the engaged position 15a shown in FIG. 1. Such rotational displacement of the assembly 16 can occur only when the terminals 30,31 are disengaged from the assembly 16. This corresponds to the pull position'of the control shaft in the above Harges et al. patent.

The central shaft 17 is rotatably mounted, and is also longitudinally displaceable. The central shaft 17 has a generally rectangular cross-section, basically with two parallel flats, as is shown in detail in my above copending Patent No. 3,219,953. The assembly 16 and the end discs 18, 19 have central openings shaped to accommodate the shaft 17 and are thus turnable thereby. The central shaft 17 extends beyond the end plate 21 Without engaging it. The inner end of the central shaft 17 is rotatably housed in a hollow tubular portion of control shaft 42 journalled in the end plate 22. A control knob 43 is secured to the outer end of the control shaft 42.

The connector plates 35, 36 have respectively an integral extended bearing 44, 44' housing the tie rods 23, 24,'respectively. The interiors of the bearings 44, 44 desirably have a bearing sleeve such as of nylon or Oilite as shown in FIG. 1 by the broken away portion of hearing 44. The plates 35, 36 are thus maintained in parallel alignment for accurate electrical engagement and disengagement action of their associated connector sections 40, 41. Further, they are readily movable along the tie rods 23, 24, with negligible friction or skewing. The plates 35, 36 are thus readily operable mechanically, in the manner to be set forth, intheir function of providing electrical connections.

In the device, controlled displacement of the connector plate 35 is effected in the reverse direction to the displacement of the other connector plate 36, by means of linkage arms 45, 46, 47. The central linkage arm 46 is pivotally mounted on a cross member 48 which is secured i to the tie rods 23, 24 by set-screws (not shown). One end of the arm 45 is pivotally secured to the top surface of the movable connector plate 35 by a screw 50 which has a collar engageable with the arm 45 and screw threads secured with the plate 35. In a similar manner, the far end of the arm 47 is pivotally secured to the connector plate 36 by a screw 50. The arm 45 is pivotally linked with one end of the central arm 46 by a screw 51.

The arm 46 is free to pivot with respect to the arm 45, with the screw 51 as the pivotal point. The head of the screw 51 overlies the top surface of the pivotal central arm 46 to secure the pivotal connection between the arms 45 and 46. The ends of the arms 46 and 47 are pivotally connected by a screw 51'. Finally, the central portion of the pivoted central arm 46 is pivotally mounted by a screw 52 on the cross member 48. The lower threaded portion of the screw 52 is engaged with a coactin-g threaded portion in the cross member 48.

The action of the pivoted linkage 45, 46, 47 is to cause the. connector plate 36 to move in a complementary manner with the connector plate 35 when actuated by the central shaft 17. When the connector plate 35 is moved to the left, for the engage or push position, in order for its connector section 40 to engage the attenuator pad 15a, the companion connector plate 36 is moved in the opposite direction, to the right, in order to establish connection between its connector section 41 and the selected attenuator pad 15a.

When the central shaft 17is moved to the right, for the disengage or pull position, the connector plate 35 is moved to the right to disengage its connector section 40 from the pad 15a. The linkage 45, 46, 47 simultaneously moves the connector plate 36 to the left to disengage its connector section 41 from the attenuator pad 15a. Such disengagement of the connector terminals 30, 31 from the attenuator assembly, permits the turning of the assembly 16 and selection of another pad through turning of the central shaft 17. The pivotal screws 50, 50', 51,51, 52 maintain the linkage assembly in proper pivotal relation for the inverse actuation of the connector plates, 35, 36.

Engagement of the central shaft 17 with the assembly 16 is made through the flattened openings centrally of the end discs 18, 19 of the assembly 16 (see FIG. 2). Thus, rotation of the flattened central shaft 17 carries with it the assembly 16 through cooperation with the flattened openings in end discs 18, 19. Also, such engagement permits shaft 17 to move axially for its push and pull a-ctuations of the connector plates 35 and 36,-withont axial displacement of the assembly .16. The assembly 16 is'desirably held against axial displacement by means such as a grooved post or collar.

Located at the side of the attenuator is a novel feature of this invention which comprises a spring-biased button which serves as a detent to retain the assembly 16 in its present angular positions. The spring-biased button 80 is mounted for reciprocation axially of the attenuator in a detent cylinder 81 fastened 'on end plate 21 by the screw 82. The button is received in the apertures 20' in end disc 18 which apertures are preferably countersunk to provide a sharp lip 83 therebetweenas shown in FIG. 1. The button 80 and cylinder 81 pass through an aligned hole 84 in connector plate35. Accordingly, the assembly 16 is positioned atvthe desired rotary angle selected for electrical engagement with the terminals 30, 31,

by operation of button 80. Heretofore, a spring and roller detent had been employed but the impact was harmful to the more delicate thin film pads. My new detent reduces impact and provides snap-action positioning of the assembly 16 when the apertures 20' are countersunk to provide a sharp lip 83 therebetween. A ball may be used instead of button'80, but care must be taken that the ball is mounted in a cylinder 81 preventing sliding of the ball relative to the desired position of the assembly when the ball is in detent. Note that the button 80 overlaps the cylinder 81 when in detent in order to assure alignment. A ball offers the advantage of rotation and reduction in binding. 1 l

A conical compression spring 60 is seated on the end plate 21 about the shaft 17. The apex of the spring is pressed against washers 62 at the end of the connector plate 35 which is thereby spring biased to the right, into normally engaged or home position. The connector section 40 is held pressed into contact with the positioned pad 15a. Through the linkages 45, 46, 47, the plate 36 and its connector section 41 are also held thereby in normally engaged position; completing a series electrical circuit with the selected attenuator pad 15a, between the connector terminals 30, 31.

An important feature of the present invention is the novel means and mechanism for automatically disengaging (the pull) and re-engaging (the push) the connector sections 40, 41 with the selected pad 15a (or other type of electrical component) of the step device. With such mechanism, direct turn in either direction for pad selection changes is renderedfeasible and practical, as will now be described:

A bisymmetrical indexing cam 65 is mounted on the shaft 17. FIG. 2 best illustrates the cam 65 which has two symmetrical cam faces 66, 67. The faces 66 and 67 each extend in an arc of and intersect at two apexes 68, 69. A set of opposed cam rollers 70, 71 are mounted on rods 72 extending transversely of the control shaft 42. The normal engagement position of the rollers 7 0, 71, with the cam 65 is at the valleys of the arcuate cam surfaces 66, 67, as seen in FIG. 1. This corresponds to the home or static position of the mechanism, and the normally engaged one for the step attenuator.

A C or E clamp 75 is seated in slits in the central shaft 17 adjacent to the back side 73 of cam 65. A similar clamp 76 is fastened on the shaft 17 adjacent to the inner side of the connector plate 35. When the cam 65 is pressed to the right, the clamp 75 will cause it to carry the shaft 17 with it. I have found that a cotter pin can be used to replace clamp 75, which may be necessary when the force exerted by spring 64 is relatively large.

The central shaft 17, being readily longitudinally displaceable, will there-upon move the connector plate 35 due to a clamp 76, which may be replaced by a cotter pin for the same reason as stated relative to clamp 75. Clamp 76 is afiixed to shaft 17 forwardly of plate 35. The plate 35 will compress the conical compression spring 60, as shown in FIG. 1 of my copending patent No. 3,219,953.

Further, displacement of the plate 35 will move the plate 36 through operation of the connecting linkages 45, 46, 47. The spacing apart of the connector plates 35, 36 in this manner fully disconnects both connector sections 40 and 41 from the previously selected pad at position a. Such condition or phase of the step attenuator will permit direct rotation of the shaft 17 to turn the assembly 16 to a new angular position, to reselect an electrical component thereof for the microwave circuit position represented by the pad 15 designated 15a in FIG. 1.

The mechanism, operated on a direct turn basis, provides the aforesaid operations and functions. The control shaft 42 is rotated by the knob 43. The cam rollers 70, 71 thereupon ride on the associated cam surfaces 66, 67. The control shaft 42, and hence the rollers 66, 67 are held against axial displacement, by C clamp 85 and compression spring 60. The cam is held against rotation by detent ring 78 and detent pin 77 as is explained below. The elongated detent pin 77 extends from the stationary end plate 22. The pin 77 normally engages with one of the semi-circular notches 79 of a scalloped ring 78 at the base of the cam 65. Thus, when rollers 70, 71 start to ride on cam faces 66, 67, cam 65 is driven to the right as in FIG. 2.

The cam 65 is confined solely to axial movement due to the pressure by the rollers 70, 71, on its arcuate surfaces 66, 67 only so long as detent ring 78 is locked by the detent pin 77. The axes of the notches 79 in the ring 78 are angularly oriented about the axis of shaft 17 to correspond precisely with the normally connected positions of the pads 15 of the assembly 16. A corresponding notch 79 is thus engaged with pin 77 for each of the selected positions 15a. The compound shape of the cam surfaces 66, 67 provides force components in both the axial and rotational directions when the rollers 70, 71 ride up on them. The rotational component is directed in the same direction as the force exerted as one turns knob 43. The axial component is directed inwardly of the structure.

The pin 77 is made long enough to hold the cam 65 in detent, or against rotation until the connector sections 40, 41 are safely disengaged from the pad 150. As seen in FIG. 1, a notch 79 of the ring 78 is intermeshed with the pin 77 when the device is in normal engagement and use, with the rollers 76, 71 seated in the valleys of the cam 65. As the control shaft 42 and the rollers 70, 71 are turned by the control knob 43, in either direction, the cam 65 is moved inwardly of the device, to the right in FIGS. 1 and 2 until the notch of the ring 78 engaging the pin 77 is withdrawn from engagement therewith. Such displacement of the cam 65 forces the shaft 17 axially inwardly of the unit because the back side 73 of cam 65 contacts the seated clamp 75 on shaft 17.

The connector plate 35 is in turn forced against the spring 60 through the clamp 76 on the shaft 17, while because of compression, the spring 68 tends to drive the shaft 17 outwardly and force the cam 65 outwardly to force ring 78 into contact with pin 77. Concurrently, the

connector plate 36 is moved to the left, away from the assembly 16 by means of the linkage 45, 46, 47. The connector sections 40, 41 are thereby disengaged from the pad 15a when the cam 65 is sufficiently displaced inwardly towards end member 19 by rotation of the control shaft 42 and the rollers 70, 71. When the assembly 16 is thus in condition to be rotated without damage to the fragile connector sections 40, 41 the engaged notch 79 of the scalloped cam ring 78 becomes disengaged from the pin 77, as shown in FIG. 2. A considerable component of rotational force is by this time 'built up on the cam surfaces 66, 67. The cam 65 is thereupon rotated. As cam 65 is fast on central shaft 17, rotation of the cam 65 turns the haft 17 which in turn rotates the assembly 16.

The specific shapes of notches 79, cam ring 78 and pin 77 determine the operation of the mechanism in an important aspect. For example, if the indexing pin terminates in a flat surface as shown in FIG. 3, and the notches are semi-cylindrical with flat faces therebetween, then, the pin 177 may come to rest on a face 180 between adjacent notches, thereby retaining the cam ring 178 (and cam 65) in its retracted push position. This will occur if only a slight torque is applied so that friction between the flat tip of the pin 177 and the flat surface of the ring 178 facing outwardly and confronting the tip of the pin 177 may cause the tip of the pin 177 to rest poised in position on the fiat face 180. This is an unusual situation which will occur only if inadequate constant torque is applied to the knob 43 and it is a byproduct of the structure of the mechanism as originally designed rather than an object of my original invention. During rotation of the cam 65, in either direction, the spring 60 tends to maintain the cam 65 biased to the left. The outer (left) side of the ring continue to press against the tip of the pin 177 during the interval of time required to turn the cam 65 and hence the ring 178 from one notch 179 to the adjacent notch in the ring 178. When alignment of the next notch with the pin 177 is reached, then the spring 60 will tend to drive the cam 65 outwardly, engaging the aligned notch 179 with the pin 177. If the knob 43 is turned very slowly and the pin 177 binds 0n the flat outer face 180 followed by reversal of torque, on knob 43, then the cam ring 178 may be turned back so that the same notch 179 will engage with the pin 177. However, this is an irregular mode of operation which would occur only if, for example, the operator were playing with the mechanism, changed his mind, or exerted insufiicient torque on knob 43.

However, as this equipment is to be employed for use in systems where reliability of equipment is paramount, the locking of pin 177 and an outer face 178 between notches 179 has been of considerable concern to me, because it has represented a limitation of this mechanism described in my copending Patent No. 3,219,953 and il- 7 lustrated in FIG. 3 herein. Thus, I have devised a novel and improved detent ring and pin configuration shown in FIGS. 1, 2 and 4, which serves to substantially eliminate the tendency of the mechanism to bind or lock between index positions by providing a snap action relationship between the parts of the attenuator mechanism. When my new detent is employed the snap action operation of the mechanism is enhanced even further to the extent that binding is substantially overcome when the mechanism is properly aligned and machined.

Referring to FIGS. 1, 2 and 4, it will be seen that the cam ring 77 has very similar shape to the cam ring 177, in FIG. 3 except that the notches 79 have countersunk rims 87 preferably tangent and the faces 88 between notches 79 have been rounded as best shown in FIG. 4 to provide a surface providing very little frictional resistance to sliding of the pin 77 across the faces 88. In addition, the pin 77 has been machined to have a slightly rounded conical tip 89 having a pitch substantially identical to the pitch of the countersink, in order to prevent wear by distribution of force and to prevent binding. The side of the pin confronting the ring 78 will slide out of a notch 79 across rim 87, then across gradually rounded face 83 and onto a second rim 87. The forces exerted longitudinally from the pin onto the ring 78 are maximum only .when the pin tip '89 is in contact with the central portion of a ring face 88. As the ring face 88 is curved, theoretically only at one point, whichmay be'referred to as top dead center will the forces be normal to the axis of motion of the cam 65. Thus, the detent will have very little stability when the pin .is passed across faces 88 and the mechanism will be very likely to drive into its normally-engaged (push) condition. The detent button 80 and the lip 83 contribute to the instability of the mechanism at top dead center, between index positions.

The axial length of the cam 65 preferably prevents its tips 68, 69 from being overridden by the rollers 70-, 71. In practice, regular turning of knob 43 may be arranged to shift the assembly 16 by several positions before the cam resets and the connector sections 40, 41 re-engage the pad then at position 15a. Slow turning of the knob would simply displace and register the next adjacent pad 15 in the circuit throug'hthe step device. The cooperation of indexing pin 77 and cam ring 78 provide assurance that the interlinked end plates and connectors 40, 41 will be held apart from the assembly 16 during rotation of cam 65 from disengagement of one notch in the ring 78 from the pin 77 to engagement of the same or another notch with the pin 77. As seen in FIGS. 1-4, the configuration of the notches 79 in ring 78 permits coaction with the pin 77 to assure sa-fe disengagement of the connectors 40, 41 from the attenuator pads until subsequent reengagement of the pad and the connector in alignment therewith, and the pin 77 and an aligned notch in ring 78. The pin thereupon permits the cam 65 to slide back into a home, or static position when the pin and a notch 79 are aligned, to permit the cam and shaft 42 to resume their static conditions and the connectors to engage with the selected and positioned pad 15a. Normally in order to advance the cam ring 78 one notch 79 with reference to pin 77, it is first necessary to turn the knob 43 through a disengagement angle of about 90", as from the position shown in FIG. 1 to the position shown in FIG. 2 in order to drive cam 65 inwardly far enough to disengage a notch in cam ring 78 from the end of pin 77, and then to rotate' the knob an additional (net) angle equal to the angle between notches e.g., if there are twelve equally spaced pads, the angular displacement therebetween will be 30 as will be the angles between adjacent ones of the 12 notches shown. Thus, in operation knob '43 would be rotated through a gross angle of say 120 and then it would be returned 90 if manual force were removed from kno'b 43.'Then spring 60 would force the cam 65 outwardly towards the knob 43 and as a result, because the cam would be pinned, the cam faces 66 and 67 would force rollers 70 and 71 back from the positions shown in FIG. 2 towards'their original positions about shaft 17 until they reached the valleys between the inclined cam faces as shown in FIG. 1. As cam 65 had been rotated, say 30,

the valleys would have been displaced by a substantially identical angle, so that the net angle of rotation of knob 43' would be a substantially identical angle, e.g. about 30. Considerably less than a 360 gross angular rotation of knob 42 will have been required to advance the central shaft 17 and pads '15 by one pad position, and the net angle would be substantially equal to the angular distance between the pads about shaft 17, e.g. 30.

If'pin 77 were substantially shorter, and connectors 40, 41 were correspondingly shorter or required to travel a correspondingly shorterdistance, then the difference between the gross angle and the net angle could be reduced substantially. That difference represents play that is necessary to permit axial displacement of the cam 65 inwardly, and the connector plates 35, 36 and connector sections 40, 41 outwardly to disengagement position with respect to the assembly.

The selective switch-over of the pads 15 by means of the knob43, is readily attained from either direction of rotation. The turning torque is normally manual as in prior known step devices. The mechanism is safeguarded from internal damage, is foolproof and rugged. The electrical connections are firm andaxially precise. The biasing spring 60 ensures static stability of operation. Additional springs may be incorporated in the step device hereof. A spring located coaxially in the cam mechanism and/ or at the linkages 45, 46, 47 may be used for furtherpositive action during switchovers; particularly in motorised remotely controlled applications, control back-lash is negligible with the use of the symmetrical. cam 65.

The direct turn step attenuator ofv this invention is rugged in construction, and maintains accuracy of alignment and full electrical engagement in adverse ambient environments. The attenuator or other component step desired is readily and directly positioned in the microwave circuit with which the step device is connected.

It is to be understood that the present invention maybe generally'applicable for step presentation of longitudinal electrical or microwave components other than attenuator pads 15.'It is also useful in coaxial switching applications. The number of switchable components, or the general shape and arrangement of the elements of the step device hereof are of course optional.

Instead of employing a pin, to cooperate with the detent ring, a detent arm or other member mounted on the frame could be employed to prevent the assembly from rotating before the cam 65 has been pushed inwardly sufficiently to permit disengagement of the connector sections 40, 41.

Other shapes of the face between the notches 79 may be employed. If, for example, the detent ring is fabricated of a very hard material which will resist abrasion, then faces 88 may be replaced by rather sharp lips across which the detent member (pin 77) will ride at top dead center.

Moreover, if the shaft 17 and the assembly are suitably angularly aligned without significant play, then the necessity for the detent button 80 may be avoided. This will require care in machining and alignment to prevent wear or use of low friction bearing surfaces in the end discs 18, 19, so that the detent ring and the assembly of pads will always be properly aligned.

I have contemplated placing the bisymmetrical indexing cam on the exterior of the frame in order to reduce the space required to house the attenuator. By locating the cam on the exterior, the cam can be located in the space required for a control knob.

Having thus set forth the nature of this invention, what I claim herein is:

1. In a direct turn step attenuator, a frame, a stepping mechanism comprising a control shaft rotatably mounted in said frame, for rotation about its longitudinal axis, a pair of rollers mounted coaxially on opposite ends, of a transverse member affixed intermediate its ends to one end of said control shaft, a central shaft coaxial with said control shaft, a bisymmetrical cam having. cam faces inclined relative tosaid longitudinal axis, said cam being affixed on said central shaft, biasing means for urging said cam and said faces thereof into contact with said rollers, said cam including a detent ring concentric with said longitudinal axis and having a plurality of peripheral notches equidistant from said longitudinal axis, a pin mounted on said frame for cooperating with said detent ring in its at rest position to engage with any se lected one of said notches in said detent ring, said detent ring and said pin cooperating in said at rest position to prevent rotation of said cam in response to rotation of said control shaft and said rollers whereby said rollers urge said cam into a retractedaxial position in response to the force exerted by said rollers on said camfaces until said pin is withdrawn from engagement with the selected notch in said detent ring thereby permitting rotation of said cam in response to further turning of said control shaft and said rollers, said biasing means preventing further axial displacement of said cam during rotation of said cam, and said detent ring and said pin cooperating to maintain said cam in said retracted axial position prior to engagement of said pin with the succeeding notch in said detent ring.

2. In a direct turn step attenuator, a frame, a stepping mechanism comprising a control shaft rotatably mounted in said frame for rotation about its longitudinal axis, a pair of rollers mounted coaxially on opposite ends of a transverse member affixed to said control shaft, a bisymmetrical cam having a pair of cam faces, said cam being affixed to a central shaft coaxial with said control shaft, and slidably and rotatably mounted in said frame relative to said longitudinal axis, biasing means, said central shaft and said cam being urged by said biasing means to provide contact between said cam faces and said rollers, said cam faces comprising several surfaces inclined relative to said longitudinal axis to provide four inclined surfaces forming two valleys normal to said longitudinal axis and on opposite sides thereof and a pair of sharp peaks on opposite sides of said axis and spaced ninety degrees from said valleys, a detent ring mounted on said cam coaxial with said central shaft and said control shaft having a plurality of notches in the periphery thereof spaced apart by a predetermined stepping angle, having axes parallel to said longitudinal axis and equidistant therefrom, a cylindrical pin mounted at one end on said frame with an axis parallel to said longitudinal axis and equidistant therefrom relative to said axis of said plurality of notches, the diameter of said pin and said notches being matched in contour to fit firmly, said pin extending beyond the ends of said notches nearer its aflixed end by a predetermined length during full insertion of said pin within said notches, said pin having a substantially conical surface at the end thereof opposite its afiixed end, said conical surface being substantially concentric with the cylindrical axis of said pin, the surface of said cam ring facing the affixed end of said pin being generally fiat and defining a plane normal to the cylindrical axis of said pin, the bearing surfaces for said conical tip of said pin on said cam ring between said notches being inclined relative to said conical tip to provide an unstable relationship between said pin and said ring under the biasing force of said biasing means, thereby tending to cause said pin and cam ring to slide under the biasing force relative to each other to permit said cam to return into full engagement of said pin and a selected one of said notches upon release of torque from said control shaft.

3. In a microwave step device comprising an assembly of circuit pads longitudinally oriented in a cylindrical array and rotatably mounted in the device with a pair of connector holders mounted apart across said assembly, a terminal connector carried by each said holder for selective circuital connection with the adjacent terminal end of any selected one of said pads said assembly of circuit pads including a pair of end discs, each of said end discs defining a plurality of apertures adapted to support the ends of said circuit pads to provide rigid support therefor, and adapted to provide access by each said terminal connector to said adjacent terminal end of any selected one of said pads, said holders being individually displaceable longitudinally to engage and disengage said connectors from the pads, spring means arranged to normally bias said connector holders inwardly toward said assembly to maintain said terminal connectors in circuital engagement with the selected pad, cam means supported for longitudinal displacement, cam actuator means coactable with said cam means, a control shaft extending from said device for operating said actuator means against said cam means, said cam means being thereupon moved longitudinally of said array upon turning of said control shaft, said connector holders being mechanically associated with said cam means to effect displacement of the holders outwardly of said assembly and disengage the respective connectors from said selected pad upon the operation of said cam actuator by said shaft, and means mechanically responsive to further turning of said control shaft for shifting the angular position of said assembly in correspondence with the further turning of said control shaft for positioning a successive pad for circuital engagement, whereupon said spring means presses said connector holders towards said assembly to effect engagement of said connectors with the successively positioned pad, detent means for cooperating with said cam means for accurately locating a selected pad in substantial axial alignment with said connectors comprising a spring-biased projecting member of rounded contour on the surface confronting one end disc of said paid of end discs, said projecting member being slidably housed with a detent spring in a hollow housing aflixed to said device, said one end disc being shaped to define countersunk surfaces concentric with said apertures on the side thereof confronting said projecting member, each said countersunk surface being substantially tangent to adjacent countersunk surfaces to define sharp lips between said apertures along the path of contact between said one end disc and said projecting member during turning of said assembly, said detent spring, said projecting member and said one end disc thereby cooperating to urge said assembly into positions for circuital engagement selectable by turning of said assembly to slide said sharp lips across said projecting member towards an other detent position.

References Cited UNITED STATES PATENTS 2,547,616 4/1951 Beekman 74-826 X 3,219,953 11/1965 Schwartz 3338l ELI LIEBERMAN, Primary Examiner.

HERMAN KARL SAALBACH, Examiner.

R. F. HUNT, Assistant Examiner. 

1. IN A DIRECT TURN STEP ATTENUATOR, A FRAME, A STEPPING MECHANISM COMPRISING A CONTROL SHAFT ROTATABLY MOUNTED IN SAID FRAME, FOR ROTATION ABOUT ITS LONGITUDINAL AXIS, A PAIR OF ROLLERS MOUNTED COAXIALLY ON OPPSITE ENDS OF A TRANSVERSE MEMBER AFFIXED INTERMEDIATE ITS ENDS TO ONE END OF SAID CONTROL SHAFT, A CENTRAL SHAFT COAXIAL WITH SAID CONTROL SHAFT, A BISYMMETRICAL CAM HAVING CAM FACES INCLINED RELATIVE TO SAID LONGITUDINAL AXIS, SAID CAM BEING AFFIXED ON SAID CENTRAL SHAFT, BIASING MEANS FOR URGING SAID CAM AND SAID FACES THEREOF INTO CONTACT WITH SAID ROLLERS, SAID CAM INCLUDING A DETENT RING CONCENTRIC WITH SAID LONGITUDINAL AXIS AND HAVING A PLURALITY OF PERIPHERAL NOTCHES EQUIDISTANT FROM SAID LONGITUDINAL AXIS, A PIN MOUNTED ON SAID FRAME FOR COOPERATING WITH SAID DETENT RING IN ITS AT REST POSITION TO ENGAGE WITH ANY SELECTED ONE OF SAID NOTCHES IN SAID DETENT RING, SAID DETENT RING AND SAID PIN COOPERATING IN SAID AT REST POSITION TO PREVENT ROTATION OF SAID CAM IN RESPONSE TO ROTATION OF SAID CONTROL SHAFT AND SAID ROLLERS WHEREBY SAID ROLLERS URGE SAID CAM INTO A RETRACTED AXIAL POSITION IN RESPONSE TO THE FORCE EXERTED BY SAID ROLLERS ON SAID CAM FACES UNTIL SAID PIN IS WITHDRAWN FROM ENGAGEMENT WITH THE SELECTED NOTCH IN SAID DETENT RING THEREBY PERMITTING ROTATION OF SAID CAM IN RESPONSE TO FURTHER TURNING OF SAID CONTROL SHAFT AND SAID ROLLERS, SAID BIASING MEANS PREVENTING FURTHER AXIAL DISPLACEMENT OF SAID CAM DURING ROTATION TO SAID CAM, AND SAID DETENT RING AND SAID PIN COOPERATING TO MAINTAIN SAID CAM IN SAID RETRACTED AXIAL POSITION PRIOR TO ENGAGEMENT OF SAID PIN WITH THE SUCCEEDING NOTCH IN SAID DETENT RING. 